All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. If this amount of 20 are purely administrative fees which are not exaggerated, and it is not a way of getting around Ribaa (interest or usury), then this is permissible, otherwise it is forbidden. If it is the permissible case, then it is permissible to pay more than this amount as long as one does this by his own choice and will, in order to cooperate and support his Muslim brothers. Allaah Knows best.